Pressure device and seal for filter belt machines

ABSTRACT

A pressure device for machines for dewatering or filtering of suspensions, sludges or the like or for material to be pressed for the exertion of surface pressure on at least one circulating pressure belt which can be provided for supporting an equally circulating filter belt, which pressure device consists of an essentially completely hollow pressure bladder in the form of a closed frame in particular of essentially quadrangular shape viewed in top view of the pressure belt, which pressure bladder is subjectable to pressure medium and forms a very small, self-adjusting gap on the edge.

The invention relates to a pressure device for machines and to machinesprovided therewith for dewatering or filtering of suspensions, sludges,in particular fibrous material or pulp suspensions or the like, or formaterial to be pressed, for exerting pressure on at least onecirculating pressure belt which can be provided for supporting at leastone also circulating filter belt, preferably screen belt.

For the further processing or the disposal of various sludges or fibroussuspensions accumulating in industry or community facilities, priordewatering is necessary. It is important in this to obtain high drymatter contents, either for further use or the disposal of this materialor for the subsequent drying of the product. In the latter case, theenergy required for mechanical pressing is essentially lower than thatrequired for thermal drying, so that one aim of dewatering is to obtainthe highest possible contents of dry matter by mechanical means.

For dewatering according to the principle of the double screen beltpress, two values, above all, are determining for the dewatering result,namely, the dewatering time and the dewatering pressure, both having tobe adapted to the material to be dewatered, and moreover, the highestpossible values for pressing time as well as pressing pressure are aimedat.

In conventional belt presses, the pressing power is applied to the twofilter belts either via looped rollers as a result of screen tension orsocalled press nips, with a linear support of the press belts by meansof press rollers. There are also supports of the filter belts in theform of perforated plates, although sliding friction occurs betweenthese plates and the moving screen belts, so that the pressing forcesare limited, on the one hand, and high frictional forces withcorresponding stress and abrasion of the screen belts and high drivingpower requirement result, on the other hand.

Similar problems also result when circulating pressure belts areinterposed between the screen belts and stationary pressure plates orthe like, in this case, however, between the pressure belts and thepressure plates or the like.

It is the object of the invention to avoid these disadvantages and toprovide a pressure device or a machine provided therewith which permitsthe exertion of a continuous pressing power over the entire or a largersurface of the press cake at low energy requirement.

This object is achieved according to the invention in a pressure deviceof the type initially mentioned if at least one, very largely,conveniently completely, separate, essentially closed, deformable andessentially completely hollow pressure bladder of flexibly elasticmaterial having tensile strength in the form of a closed frameconveniently adapted to the surface facing it or the surface abutting itof the supporting or pressing device and thus abutting this surface, inparticular of quadrangular, for instance rectangular shape viewed in topview onto the filter belt or pressure belt, conveniently with roundedcorners, is arranged, a gap, advantageously a small gap in relation tothe height of the pressure bladder, being independently adjustablebetween pressure bladder and pressure belt, at least by admittingpressure medium into the pressure space formed by the frame-shapedpressure bladder and the inner space of the pressure bladder. The hollowpressure bladder has an essentially closed cross section.

By the arrangement according to the invention, it is achieved that evenat fluctuating thickness of the material to be pressed, an automaticadjustment takes place and the pressing power thus remains unchanged.

According to an embodiment of the invention, it is provided that thehollow pressure bladder is at least partially a component of a wall ofan essentially completely enclosed pressure space to which pressuremedium, in particular pressure fluid (liquid) can be admitted and whichis arranged on one side of the pressure belt, the hollow pressurebladder being arranged at a distance from the wall at least on exertionof pressure by the admission of pressure medium, thus forming a gapthrough which pressure medium can escape for lubricating. In thisembodiment, fluid friction without contact of solid parts is obtainedbetween the moving belts and the stationary parts, so that frictionforces and thus wear and driving power are kept very low. The gap formedbetween the hollow pressure bladder and the pressure belt, which gap isvery small in relation to the thickness of the pressure belt, adjustsitself independently on being subjected to pressure by the pressuremedium. In the inactive position, i.e. when the machine is not inoperation, this gap optionally need not be present.

The hollow pressure bladder can consist of flexibly elastic materialhaving tensile strength, in particular of fabric-reinforced plasticmaterial or rubber. The hollow pressure bladder can also be formeddouble-walled, for instance of an inner skin of compression-proofelastic material and an outer skin of material having tensile strength.

It is convenient if the pressure space adjacent the pressure belt isjointly defined on all sides by the pressure belt and the hollowpressure bladder which is shaped frame-like for this purpose, with themarginal zones of the pressure space being particularly closed againstthe hollow pressure bladder. The hollow pressure bladder is preferablyformed auto-adjustingly in its marginal zones.

It is convenient to form the hollow pressure bladder viewed in plan viewonto the filter belt or pressure belt essentially quadrangular,preferably rectangular or square, with the corners preferably beingrounded off.

It is further convenient to fasten the hollow pressure bladder by meansof at least one frame on a stationary support, this frame alsopreferably being formed essentially quadrangular, for instancerectangular or square. The frame can be at least partially hollow. Forfastening the hollow pressure bladder on the support of the machine, itis convenient to clamp the hollow pressure bladder between two frames.For maintaining a constant pressure or for compensating pressure, it isconvenient if the pressure space adjacent the pressure belt and thepressure space in the interior of the hollow pressure bladder areconnected to one another by means of at least one opening.

In order to be able to adjust different pressures in the pressure spaceand in the interior of the hollow pressure bladder, it is convenient toclose the pressure space adjacent the pressure belt and the pressurespace in the interior of the hollow pressure bladder against each otherand make them suitable for the admission of pressure medium, optionallyof different pressures, through separate inlets or bores.

In order to prevent friction between the hollow pressure bladder and thepressure belt in the event of breakdown, for instance at failure ofsupply with pressure medium, it is convenient to provide the hollowpressure bladder in the gap between it and the pressure belt with atleast one wear-protection sleeve abutting the pressure belt and made ofabrasion proof, well gliding material, in particular plastic material,for instance polytetrafluorethylene or polyurethane.

In order to prevent loss of pressure medium, it is convenient to provideat least one seal of rubber or plastic material gliding along thepressure belt outside of the hollow pressure bladder preferably incirculating direction of the pressure belt and transversely theretospacially behind or laterally of the hollow pressure bladder, i.espacially behind or laterally of the gap formed between the hollowpressure bladder and the pressure belt at least on admission of pressuremedium or in operation, with at least one opening for the discharge ofpressure medium escaping through the gap being provided between thehollow pressure bladder and the seal. The gliding seal advantageouslycompletely encloses the outside of the pressure bladder.

It is also possible to provide two or more hollow pressure bladdersspacially or tightly adjacent in circulating direction of the pressurebelt, in which case it is convenient for the gliding seal to enclose theentire group of pressure bladders.

The invention is explained in the following by means of exemplaryembodiments under reference to the accompanying drawings.

FIG. 1 shows a diagrammatic view of a dewatering machine with thepressure device according to the invention;

FIG. 2 shows a sectional view through the pressure bladder along lineII--II in FIG. 3;

FIG. 3 shows the shape and fastening of the pressure bladder accordingto FIG. 2, 4 and 5 schematically in plan view in reduced scale;

FIG. 4 shows a sectional view of the pressure bladder along line IV--IVin FIG. 3 of a special arrangement for pressure feed as well as theplacing of a wear-protection sleeve;

FIG. 5 shows a sectional view along line V--V in FIG. 3 through apressure bladder with a gliding seal arranged behind it; this sealencloses the pressure bladder on all sides; if several pressure bladdersare provided, this seal encloses all pressure bladders or the group ofpressure bladders completely on the outside;

FIG. 6 shows a further variant with a half-bladder.

FIG. 7 shows an alternative embodiment in which the pressure bladder hasa double wall; and

FIG. 8 shows an alternative embodiment having two pressure bladders.

The dewatering machine of compact construction shown diagrammatically inFIG. 1 comprises a lower endless filter belt 1 and an upper endlessfilter belt 2 between which the material to be dewatered is made topass. The lower filter belt 1 is formed as a supporting screen and ispassed over a plurality of rollers, i.e. a screen regulating roller 11,a reversing roller 14 and a tensioning roller 13. The upper filter belt2 is formed as a cover screen and is passed over guide rollers 14', atensioning roller 13' as well as over a regulating roller 11'.

The material to be dewatered is charged by a charging means 7 onto thelower filter belt 1 so that a cake of approximately uniform thickness isformed to be dewatered between the two filter belts 1,2.

In the pressing zone, the two filter belts 1, 2 are supported bycirculating, endless pressure belts 3 and 4. The lower pressure belt 3as well as the upper pressure belt 4 are passed over reversing rollers9, 9', tensioning rollers 10, 10' and regulating rollers 11", 11'". Thedrive can be effected, for instance, by means of rollers 8, 8'. At thebeginning and at the end of the press line, smaller reversing rollers12, 12' are arranged. The pressure belts 3, 4 are made of elasticmaterial which is impermeable to water and liquids, such as rubber orplastic material. The supports 5, 6 serve for exerting the requiredpressing power on the pressure belts 3,4 and further on the filter belts1,2 and thus on the press cake lodged therebetween. These supports 5,6take up the entire pressing force and are therefore of very stableconstruction. On either side of the dewatering machine, the upper andlower supports are connected to one another in order to achieve atransmission of the entire forces by a short way. This has the advantagethat the very high pressing forces do not have to be transmitted to themachine frame, so that this machine frame can be of comparativelylightweight and inexpensive construction. A special hydrostatic pressuredevice shown in detail in FIG. 2 serves for the transmission of theforces from the supports 5,6 to the moving pressure belts 3,4.

FIG. 2 diagrammatically shows the pressure device in section along lineII--II in FIG. 3. For this purpose, a pressure bladder 15 is bent inU-shape and made of elastic material having tensile strength, such as aweb of fabric-reinforced plastic material or rubber, and provided on thestationary support 6; this pressure bladder 15 is attached by means ofan intermediary frame 16 and a clamping frame 16' in such a way that aninterior space 18 sealed all around and kept at a certain superpressureis formed.

The surface pressure is exerted on the moving pressure belt 4 in such amanner that a pressure medium, such as, for instance, water, is pumpedthrough an inlet 20 into a pressure space 17 adjacent the pressure belt4. A small portion of the amount of water introduced escapes through thevery small, circumferentially extending gap 21. This amount, however, isconstantly replaced through the inlet 20 by means of a pump not shown indetail so that a constant pressure of the desired value is maintained inthe pressure space 17.

A connection between the pressure space 17 adjacent the pressure belt 4and the interior space 18 of the pressure bladder 15 is established by abore 22. By this bore 22, the pressure in the interior space 18 of thepressure bladder 15 and in the pressure space 17 is kept equal, so thatthe elastic pressure bladder 15 is kept in equilibrium. The result ofthis special arrangement is that the width of the gap 21 automaticallyadjusts itself to a very small value in the order of magnitude of a fewhundredths of millimeters. This keeps the volume of escaping pressuremedium, for instance water, very low, which also requires very littleenergy for supplementing the pressure medium, for instance water, bymeans of the pump.

The distance between the support 6 and the moving pressure belt 4 is notconstant, but changes according to the thickness of the press cake to bedewatered and also due to the compression of the material under theinfluence of the pressing force. The embodiment described has theadvantage that the pressure bladder 15 automatically adapts itself tosuch fluctuations of thickness, so that in this case, the gap 21 alsoremains very small and that the pressure in the pressure space 17 ismaintained. This makes it possible to maintain a constant surfacepressure over the entire pressing surface although the material to bepressed is not level and shows differences in thickness.

FIG. 3 diagrammatically shows the configuration of the pressure bladders15 according to FIGS. 2, 4 and 5 in reduced scale as compared to FIGS.2, 4 and 5, in plan view, the seal according to FIG. 5 not being shown.The exemplary shape shown here is a rectangular one, with the clampingframe 16' fastened, for instance, by means of suitable, spaced screws.The pressure bladder 15 is formed, for reasons of production, not withsharp, but with slightly rounded corners.

FIG. 4 shows in sectional view along line IV--IV in FIG. 3 a specialarrangement of a pressure device. In addition to the inlet 20 for thepressure space 17, there is a separate inlet 20' for the interior space18 of the pressure bladder 15. This makes it possible to obtain slightlydifferent pressures in the pressure space 17 and in the interior spaceof the pressure bladder 15, so that a special adaptation of the pressurebladder 15 is possible, which is of advantage in some cases of use.

FIG. 4 also shows the arrangement of a wear-protection sleeve 24 ofabrasion-proof, well gliding material, in particular plastic material,for instance polytetrafluor ethylene or polyurethane. This serves forpreventing wear of the pressure bladder 15 at failure of the supply ofcompressed water or other breakdowns where it comes into contact withthe circulating pressure belt 4. This also offers the advantage that thematerials for the impermeable pressure belt 4 and the wear-protectionsleeve 24 can be optimally matched to one another in respect of glidingbehavior and no consideration need be given to abrasion in the selectionof the material of the pressure bladder 15. An additional advantageresides in the fact that in case of damage, for instance by faultyoperation, only the comparatively inexpensive wear-protection sleeve 24need be exchanged, while the pressure bladder 15 remains undamaged.

FIG. 5 shows as a further variant a sectional view along line V--V inFIG. 3 through the pressure bladder 15 with the pressure space 17 andthe interior space 18 of the pressure bladder 15. This shows a furtherseal 25 also fixed to the support 6. This seal 25 glides on the movingpressure belt 4 and serves for trapping the pressure medium escapingfrom the gap 21, so that this medium can be discharged via bores 26 andreturned to the pressure space 17 via a pump in the cycle which is notshown. This prevents a loss of pressure medium or pressure water whichresults in substantial advantages in respect of operation and cost.

The seal 25 consists of rubber or plastic material, for instancethermoplastic material, and is arranged in circulating direction and intransverse direction of the pressure belts 3,4 spacially behind these,i.e. spacially after the gap 21 between the hollow pressure belts 3,4 aswell as spacially laterally next to the pressure bladder 15.

FIG. 6 shows as a further example a different embodiment of the pressuredevice in sectional view. In this the interior space 18 is definedpartly by the pressure bladder 15 and partly by the fixed support 6. Thefastening of the pressure bladder 15 is effected by means of theclamping frames 16 and 16' which are formed essentially quadrangularlyand results in a tight connection.

FIG. 7 shows an alternative embodiment in which pressure bladder 15 hasan outer wall 30 and an inner wall 31. Inner wall 31 is formed from anelastic material, and outer wall 30 is formed from a material having ahigher tensile strength than the material used for inner wall 31.Pressure bladder 15 is attached to the device in the same manner as thepressure bladder of FIG. 2.

FIG. 8 shows another alternative embodiment in which a second hollowpressure bladder 40 is disposed around the first hollow pressure bladder15. Bladder 40 has the same frame-like shape as bladder 15 andcompletely encircles and encloses bladder 15. Bladder 40 is a attachedto the device in the same manner as bladder 15, i.e., by a frame 43 anda clamping frame 44. Frame 43 has a bore 46 which communicates theinterior space 41 of bladder 40 with the pressure space 45. Pressurespace 45 is bounded by bladder 40, bladder 15, belt 4, and stationarysupport 6. If a seal 25 is used with this double bladder arrangement,seal 25 is disposed beyond bladder 40 so as to encircle and enclose bothbladders.

In a machine with an upper pressure belt and a lower pressure belt, suchas it is shown in FIG. 1, the hollow pressure bladder described can beassociated with the upper and the lower pressure belts. The pressurebelts are formed smooth on their sides facing the pressure bladder.

The pressure device or a machine provided therewith can also be used formaterial to be pressed, in which case only pressure belts, but no filterbelts or screen belts are used. The pressure bladders or hollow framesfilled with pressure medium can be subjected to the action of pressingor supporting means with plane or concavely curved plates or surfacesfacing them., the pressure pads or hollow frames can also be arranged inhollow chambers open towards the pressure belt. The belts could alsopass over one or a plurality of roller(s), which results in a convexsupport. In this case, the closed frames formed of the hollow pressurebladders would have to be convexly curved accordingly. The material tobe pressed could also be dry material.

According to the invention, a pressure space proper is only present inthe space enclosed by the hollow frame or pressure pad and in theinterior of the frame or pad., after the zone surrounding the frame orpad, only leakage water or the like escapes through the lubricating gap21.

We claim:
 1. Apparatus for pressing and dewatering or filteringsuspensions, sludges, fibrous material or pulp suspensions, comprising:astationary support; a driven, endless pressure belt; a driven, endlessfilter belt, said apparatus being structured to press the material ontwo sides by exerting pressure on said pressure belt and on said filterbelt; a first pressure medium source; means defining a pressure spacepartially bounded by said pressure belt and said support; a firstdeformable, essentially hollow pressure bladder of flexibly elasticmaterial having an interior space, said bladder being supported by saidstationary support and being situated completely outside of saidstationary support and having the form of a closed frame viewed in topview onto the pressure belt, said bladder further bounding said pressurespace; a gap formed between said bladder and said pressure belt; meansfor adjusting the size of said gap by subjecting said pressure space andthe interior space of the pressure bladder to pressure produced by saidpressure source; a seal comprising either rubber or plastic material,said seal being disposed outside of the first hollow pressure bladderand outside of the pressure space to encircle and enclose said firsthollow pressure bladder and said pressure space; and means defining anopening in the stationary support for the discharge of pressure mediumescaping through the gap, said opening being disposed between the firsthollow pressure bladder and said seal.
 2. The apparatus according toclaim 1, wherein said pressure belt supports said endless filter belt.3. The apparatus according to claim 1, wherein said support has a flatsurface facing said hollow pressure bladder and said bladder isstructured in shape to abut said surface.
 4. The apparatus according toclaim 3, wherein said hollow pressure bladder is of substantiallyrectangular shape viewed in top view onto the pressure belt.
 5. Theapparatus according to claim 1, wherein the cross-section of the hollowpressure bladder perpendicular to the pressure belt is substantiallyclosed.
 6. The apparatus according to claim 1, wherein the hollowpressure bladder comprises either fabric-reinforced plastic material orrubber.
 7. The apparatus according to claim 1, wherein the hollowpressure bladder has an inner skin and an outer skin.
 8. The apparatusaccording to claim 7, wherein said inner skin is formed from elasticmaterial and said outer skin is formed form material having a highertensile strength than said inner skin.
 9. The apparatus according toclaim 1, wherein the hollow pressure bladder is essentially quadrangularviewed in plan view onto the pressure belt and has rounded edges. 10.The apparatus according to claim 1, further comprising a substantiallyrectangular frame for fixing the hollow pressure bladder to saidstationary support.
 11. The apparatus according to claim 10, furthercomprising a second frame, the hollow pressure bladder having two edgesand being clamped between said two frames by the edges of said bladder.12. The apparatus according to claim 1, further comprising meansdefining an opening connecting said pressure space with said interiorspace of the hollow pressure bladder.
 13. The apparatus according toclaim 1, wherein said means for adjusting comprises means defining afirst opening communicating said pressure source with said pressurespace and means defining a second opening communicating said pressuresource with said interior space of the hollow bladder, said pressurespaces and said interior space being closed against one another.
 14. Theapparatus according to claim 1, further comprising a wear-protectionsleeve of abrasion proof and well-gliding material disposed adjacent thepressure belt and reaching into said gap.
 15. The apparatus according toclaim 1, further comprising a second hollow pressure bladder disposed soas to surround said first hollow pressure bladder, said seal completelysurrounding both said pressure bladders.
 16. The apparatus according toclaim 1, wherein the cross-section of the hollow pressure bladderperpendicular to the pressure belt is open, said interior space beingbounded by said bladder and said stationary support.
 17. Apparatus forpressing and dewatering or filtering suspensions, sludges, fibrousmaterial or pulp suspensions, comprising:a stationary support; a driven,endless pressure belt; a driven, endless filter belt, said apparatusbeing structured to press the material on two sides by exerting pressureon said pressure belt and on said filter belt; a first pressure mediumsource; means defining a pressure space partially bounded by saidpressure belt and said support; a first deformable, essentially hollowpressure bladder of flexibly elastic material having an interior space,said bladder being supported by said stationary support and beingsituated completely outside of said stationary support and having theform of a closed frame viewed in top view onto the pressure belt, saidbladder further bounding said pressure space; a gap formed between saidbladder and said pressure belt; means for adjusting the size of said gapby subjecting said pressure space and the interior space of the pressurebladder to pressure comprising means defining a first openingcommunicating said first pressure source with said pressure space andmeans defining a second opening communicating a second pressure sourcewith said interior space of the hollow bladder, said pressure space andsaid interior space being closed against one another; a seal comprisingeither rubber or plastic material, said seal being disposed outside ofthe first hollow pressure bladder and outside of the pressure space toencircle and enclose said pressure bladder and said pressure space andmeans defining an opening formed in the stationary support for thedischarge of pressure medium escaping through the gap, said opening inthe stationary support being disposed between the hollow pressurebladder and said seal.